1. Field of the Invention
The field of the invention relates to devices for creating a three-dimensional image using a coherent, monochromatic electromagnetic radiation (LASER). The invention relates to a new and improved fiber optic LADAR (LASER detection and ranging) system. It can be used to provide information to guidance systems for vehicles such a guided missiles. This system is based upon inputs from optical fibers distributed at various locations on the vehicle, and a scanning laser transmitter. A plurality of the optical fibers receive and transmit to three photodiode detectors intermittent light energy from the scanning LASER energy reflected off the target. A plurality of the optical fibers receive individual reflected signals from the target and transmit them to the detectors, which provides input to a microprocessor which determines the elevational, azimuthal direction and range to the target to a high degree of accuracy. The individual pulse information can then be combined with other pulses to form a three dimensional image. A method for utilizing the system is disclosed.
2. Description of the Prior Art
The use of optical fibers for transmitting tracking information is known, but often has been applied to transmission of such information rather than collection thereof. For example, U.S. Pat. No. 4,952,042, issued Aug. 28, 1990 to Pinson and assigned to The Boeing Company, discloses the use of optical fibers for transmitting information obtained by a telescope mounted on a gimbal in the forward end of a missile to a camera mounted further back in the missile. Similarly, U.S. Pat. No. 5,052,635, issued Oct. 1, 1991, to Paulet and assigned to Thomson-CSF, discloses the use of optical fibers for transmitting remotely transmitted missile guidance information from a sensor on an unpropelled aerodynamic carrier connected to the body of the missile by a flexible link.
U.S. Pat. No. 4,923,276, issued May 8, 1990, to Wells and assigned to Teledyne Industries, Inc., discloses a fiber optic telescope including an optical train having a plurality of tapered optical fibers arranged in a plurality of cascading stages. Wells' optical fibers concentrate and magnify the incoming light waves by both their tapered form and the cascading stages. Wells requires a large number of tapered optical fibers to be combined in a concentrating relationship to amplify the signal received for use in obtaining information on location of the source of light upon which it is trained.
The use of optical target detectors utilizing laser light is disclosed in U.S. Pat. No. 5,014,621, issued May 14, 1991 to Fox, et al. and assigned to Motorola, Inc. This patent utilizes a star coupler to automatically align pencil laser beams upon a target, and to track the target based on reflections of the laser light.
The use of missile referenced beamrider guidance links is disclosed in U.S. Pat. No. 4,696,441, issued Sep. 29, 1987 to Jones, et al. and assigned to the United States of America. Jones et al. discloses a laser beam in which the strength of the beam is formed into a gaussian cross section, the beam is directed upon a target at short range, detectors on an in-flight missile detect and measure the strength of the laser beam, and a guidance system guides the missile along the beam by adjusting the guidance controls to maximize the detected strength of the beam. The Jones et al. missile includes at least one laser detector mounted outside the central longitudinal axis of the missile and requires a reference beam.
A detector device for detecting the presence and originating direction of laser radiation is disclosed in U.S. Pat. No. 4,825,063, issued Apr. 25, 1989 to Halldorsson et al. and assigned to Messcrschmitt-Bolkow-Blohm GmbH. The Halldorsson device includes a plurality of discrete light collection optics, each discrete optic being capable of gathering laser radiation over a certain solid angle, which overlaps the solid angle of its neighbors. The discrete optics are mounted together in a head, regularly arranged in azimuth aligned planes and elevation aligned planes. In Halldorsson's device, first, second and third wave guides are coupled to each discrete optic, with all first wave guides having identical lengths, shorter than the second and third wave guides. The lengths of the second and third wave guides are of increasing length in the direction of increasing azimuth and elevation angle, respectively, in order to form different transit times. In Halldorsson's device, first, second and third detector stages have opto-electrical transducers and are coupled respectively to the first, second and third wave guides. Transit time measuring circuits are coupled to the first, second and third detector stages which determine, respectively, the total time between detection by the first detector stage and the second and third detector stages. Based upon the times of arrival, the azimuth angle and the elevation angle of the incident laser radiation is determined. Halldorsson's system is limited by its use of discrete optics, a high speed counter for measuring time, and its use of a head for mounting its plurality of neatly aligned azimuth and elevation planes of identical discrete optics. Halldorsson's degree of accuracy is limited by the measurement only of transit time differences.
U.S. Pat. No. 5,784,156 issued Jul. 21, 1998 to Nicholson, describes a fiber optic system for laser guided missiles which uses an array of apertures disposed along the vehicle in non-uniform locations. Each aperture is provided with a set of fibers including start and stop fibers. The fibers receive incoming radiation, transmit the radiation as optical signals to start and stop detectors. The detectors measure a signal strength and time delay related to the length of the start and stop fibers through which the optical signals have been transmitted. This information is later used by a microprocessor to calculate the direction to the radiation source relative to the vehicle. The above mentioned patents are incorporated by reference as though set forth in full.
None of the systems disclosed in these prior art patents provide the features disclosed in the following specification.